This proposal is directed toward the study of the innate immune response through the Toll signal transduction pathway. By examining the way in which Toll pathway functions in response to infectious diseases and by determining ways in which this facet of innate immunity may regulate adaptive immunity, it may be possible to augment, extend, and prolong the immune response. In order to examine the role of each protein in the Toll pathway, a new antisense technology, in which an alternative type of oligonucleotide (morpholino oligos) blocks translation of mRNA transcripts, will be used to produce zebrafish knock-downs. The morpholino knock-downs are easy to design and only require sequence information in the 5' untranslated region (UTR), thirty to forty bases upstream from the translational start site (AUG). This new technology is extremely flexible and will afford the rapid generation of knock-down fish. In addition, the morpholino translation block allows for quick and easy application of combinations of two or three oligos to generate knock-down zebrafish. The SPECIFIC AIMS for this grant are: 1. To generate morpholino zebrafish knock-downs of the Toll signaling pathway 2. To challenge the knock-downs with viral and bacterial zebrafish pathogens By examining the Toll signaling pathway in the zebrafish and determining its role in protective immunity against pathogens, we will gain a more complete understanding of the impact of innate immunity on the development of the immune system and how this pathway has helped to give rise to the formation of an adaptive immune response.